The present invention relates to a segment-type numeric liquid crystal display (hereinafter referred to as an "LCD") device capable of switching between two or more display colors.
Prior numeric LCD devices capable of displaying two or more display colors include dot-matrix font displays. FIGS. 1A and 1B are fragmentary front elevational and cross-sectional views, respectively, of such a dot-matrix LCD device. As shown in FIGS. 1A and 1B, the dot-matrix LCD device includes confronting transparent substrates 1a, 1b, a plurality of elongated transparent electrodes 2a, 2b, . . . , (generally referred to as "2"; only numerals out of similar combinations of numerals and alphabetic suffixes will similarly be used below); a plurality of transparent electrodes 3a, 3b, . . . made, for example, of indium oxide formed on inner surfaces of the transparent substrates 1a, 1b; a liquid crystal layer 4 sandwiched between the transparent substrates 1a, 1b; and a seal 5 made of epoxy resin including a spacer (not shown) made of alumina powder for maintaining the thickness of the liquid crystal layer 4 in a range of 1 to 100 .mu.m.
The elongated transparent electrodes 2, 3 are disposed in mutually crossing relation with the liquid crystal layer 4 interposed therebetween. Lead electrodes 6a, 6b, . . . are formed on the transparent substrate 1a and serve as lead lines for the elongated transparent electrodes 2. Lead electrodes 7a, 7b, . . . are formed on the transparent substrate 1b and serve as lead lines for the elongated transparent electrodes 3.
Striped transparent color layers 8a, 8b are formed on the elongated transparent electrodes 3, the layers 8a, 8b being colored alternately in red, green, red, green, . . . , for example. The LCD device is denoted in its entirety by 100.
A twisted nematic liquid crystal display layer having a positive dielectric anisotropy is employed as the liquid crystal layer 4, and the LCD device 100 is sandwiched between two polarizers so that it appears in a normally dark state. The assembly is illuminated with a light source such as a fluorescent lamp (not shown) which is located behind the LCD device and which emits light including components of red and green. A prescribed voltage is applied to the liquid crystal layer 4 through the crossing electrodes 2, 3 via the external lead electrodes 6, 7.
When the voltage is applied, crossing portions (hereinafter referred to as "rectangular patterns") of the electrodes 2, 3 are rendered transmissive. Therefore, when the LCD device is viewed from the side opposite the fluorescent lamp, the colored layers corresponding to the red rectangular patterns appear red, while the colored layers corresponding to the green rectangular patterns appear green.
Multicolor numeric display is effected, for example, by a five-by-seven matrix of dots, each composed of a pair of rectangular patterns having red and green colored layers. For displaying a numeral in red, five-by-seven rectangular patterns having red colored layers are used, and for displaying a numeral in green, five-by-seven rectangular patterns having green colored layers are used. When displaying a numeral in mixed red and green colors, both of the five-by-seven rectangular patterns are used.
Voltages are applied to the lead electrodes 6, 7 which will cause the rectangular patterns to light (be rendered transparent) in conformity with a desired numeral to be displayed.
It is usual to drive the dot-matrix LCD device by multiplexing using seven or more scanning lines employing a voltage averaging process.
The multicolor numeric display using a conventional dot-matrix LCD device as described above has however suffered from the following disadvantagaes:
(i) The number of lead electrodes required for displaying any numeral in one digit is large (7+5.times.2), and ten more lead wires are necessary for each additional numeric position to be displayed, resulting in complex connections to driver circuits.
(ii) The device is required to be driven by multiplexing of a relatively high order, and an operational margin is narrow, resulting in a poorer display performance than can be obtained with a segment-type LCD device.